Control for discharge devices



P 2, 1947' G. E. GUSTAFSON 2,426,680

I CONTROL FOR DISCHARGE DEVICES Filed Jan. 13, 1944 ll V INVENTOR FIG 6FIG. 1

FIG 2 =4 GILBERT E.GUSTAFS'ON HIS ATTORNEY Patented Sept. 2, 1947CONTROL FOR DISCHARGE DEVICES Gilbert E. Gustafson, River Forest, 111.,assignor to Zenith Radio Corporation, a corporation of IllinoisApplication January 13, 1944, Serial No. 518,071

7 Claims.

This invention relates to a high gain amplifier, and more particularlyto a gain control for such an amplifier.

It is desirable to make portable radio and hearing aid apparatus ofsmall size and with the least number of parts for the purposes ofconvenience in carrying and economy in manufacture, In such apparatusinput signals must usually be amplified greatly and in controllableamount for accomplishing the purposes of the apparatus. The desirablequalities of smallness are better realized when the amplification ofeach stage is high and when the number of stages is a minimum.

It is therefore an object of this invention to provide a small high gainamplifier including an improved means for controlling the gain.

A further object of the present invention is to provide such a new andimproved gain. control means in a regenerative high gain amplifier.

Still another object of the present invention is to provide a new andimproved gain control, for a high gain regenerative amplifying stage,arranged to prevent oscillation of the amplifying stage.

The operating expense for replenishing batteries'in a hearing aidcircuit is relatively large. In the mass production of hearing aids foruniversal use by persons having different degrees of deafness, it isdesirable to take into account theiact that some people require greatervoltage amplification in the hearing aid circuit than others. Forpurposes of economy, a person who requires a relatively small amount ofamplification for satisfactor hearing should not be required to bear therelatively large operating expense of one who requires greater amplification for satisfactory hearing. It is therefore another object of thepresent invention to provide a control in an electron discharge devicenot only for controlling the amount of gain in such device but also forcontrolling simultaneously the amount of space current flowing throughthe device such that relatively small space current flows when the gainis small, and, conversely, relatively large space current flows when thegain is large. 7

Yet another object of the present invention is to provide a new andimproved gain control for a high gain regenerative amplifying stage inwhich such gain control serves also as a means for reducing the amountof current flowing to such amplifying stage.

The features of the present invention which are believed to be novel areset forth with par- (Cl. 179---17l) ticularity in. the appended claims.This invention itself, both asrto its organization and manner ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawing in which: I I

Figure 1 shows. an improved hearing aid circuit incorporating a highgain amplifier circuit arranged in. accordance with the presentinvention;

and I Figs. 2 1107, inclusive, are modifications thereof.

In Fig. 1 there is illustrated an improvedhear ing aid circuit,incorporating a high'gain amplifier including electron discharge deviceiii and a second amplifier including electron discharge device M. Thetwo amplifiers successively amplify signals from microphone H andimpress such amplified signals on sound reproducing device I2 inlinearly amplified form.

Sound waves impinging on microphone H are transformed into electricalvariations in the main control electrode circuit of discharge device Hi.The microphone may, for example, be of the piezoelectric type asillustrated, or it may be of the magnetic type. The device 1!) greatlyamplifies electrical variations produced by microphone H and theamplified electrical variations are further amplified by electrondischarge device 14 before being applied to the sound reproducing devicel2.

Microphone H, which produces electrical variations in response to soundWaves impinging thereon, is connected between the main. control grid I5and the grounded filamentary cathode of discharge device 19; and a gridleak resistance It is co-nnected'in parallel circuit relationship withmicrophone IE. It is noted that substantially no grid current flowsthrough resistance is since the grid !5 is at negative potential Withrespect to the cathode of device IE3, such negative bias potential beingprovided by connecting grid !5 through resistance 6 to the groundednegative terminal of source 43 having its terminals connected toopposite terminals of the cathode of device 10.

Electron discharge device E E3 is of the pentagrid type in commercialuse andv may, for example, be of the type commonly known as the 135. Theparticular elements of this device Hi, however, are connected in alinear high gain amplifier circuit in a novel manner'not heretoforeknown. This invention is not limited to the use of a discharge device ofthe type commonly known as the 1R5, but within the scope of the. presentinvention amplifying discharge device I4.

any discharge device which performs equivalent functions is suitable.Large gain is realized when device I I3 is connected in the mannerhereinafter I described and such large gain is substantially independentof the amplitude of a signal applied between the main control grid I5and cathode of discharge device I0.

In general, device It! is connected so as to be effectively twoamplifiers in cascade with regeneration between the two amplifiers. Inaddition to the main control grid I5, discharge device I'U' has what istermed a second control grid I8, a suppressor grid I9 connected to thecathode, a

main anode 25, and a pair ofscreen electrodes 2I and 22 on oppositesides ofthe second control grid I8.

Operating continuous potentials for device I are supplied from a voltagesource 23 whose negative terminal is grounded and whose positive ter-'minal is connected to the main anode '20 of discharge device I through aseries circuit including adjustable voltage dropping and gain controlresistance 24 and output coupling resistance 25.

Electrodes 2| and 22 are connected together and are maintained positivewith respect to the oathode'of device II! by connection to the positiveterminal of voltage source 23 through the series aircuit includingvoltage dropping and gain'control resistance 24 and coupling resistance26. The continuous operating potential of the second control grid I8 isstabilized by connecting it to ground and the cathode of dischargedevice I i through resistance 21.

When alternating currentsignals are impressed between the'main controlgrid I and cathode'of discharge device I0, substantially all of thealter-1 nating output voltage appears across the output '1 couplingresistance 25, a by-pass capacitance 28 of of, discharge device ID areimpressed on the second control grid I8 through a coupling capacitance29 connected 'therebetween'.

Therefore, alternating voltages applied directly to control grid I5 andindirectly to control grid IB cause alternating output signals to appearacross resistance 25, which output signal are then, applied to the gridcircuit of another linearly Coupling 'capacitance 31 and inputresistance 32 are-connected in series and the series circuit formedthereby is connected in parallel circuit relationship to the'seriescircuit formed by output coupling resistance 25 and low reactanceby-pass capacitance '28. Capacitance 3I is of relatively low reactanceand serves essentially as a means for blocking the flow of continuouscurrent from source 23 to resistance 32. The alternatingvoltagedeveloped across resistance 32 through condenser 3I isapplied'betweenthe grid and cathode of discharge device I4 so as to control the spacecurrent therein, which current normally flows due to the fact thatvoltage source 23"is connected between the plate and cathode ofdischarge device I4 through theprimary winding 34 of an outputtransformer 35.

Discharge device I4 is preferably ofthe pentode type having itssuppressor grid connected to the voltagedropping resistance 36. Thescreen grid is maintained at constantpotential in the presence ofsignals of frequency corresponding to audio frequencies by means of lowreactance bye pass capacitance 31, which is connected between the screengrid and cathode of device I4.

Alternating voltages developed across input resistance 32 are amplifiedlinearly by discharge device I4, and appear across the secondary winding39 of transformer 35 which is connected to impress those amplifiedvoltages on the sound, reproducing device I2 which is connected acrossthe terminals of secondary winding 39.

The filamentary cathodes of discharge devices wand I4 are preferablyheated by current flowing therethrough as shown in Fig. 1. in such casethe cathodes of discharge devices I0 and I4 are connected in parallelcircuit relationship to voltage source 49. It is understood of coursethat, if desired, the filamentary cathodes of devices In and 64 may beconnected in a series circuit with source 46 for heating purposes andfor obtaining suitable-grid biasing potentials. I

The circuit thus far described is especially use,- ful as a hearing aidcircuit and, because of the high gain obtained by the use of dischargedevice Ill, only two discharge devices requiring small space current arenecessary for good performance. Because of the high gain obtained fromthe use of discharge device I5, a highly efiicient V and useful hearingaid circuit is provided which requires a small current drainfrom'voltage source 23. This is particularly truewhen, as in thisinstance, resistances 24,25 and'26are relatively large. thereto andfeatures thereof, exclusive ,of the variable volume control resistance24, are described and claimed in the copending application of John G.Prentiss, 'Se'rial N0; 504,958, filed October 4, 1943, and assigned tothesame assignee as the present application.

A feature of the present invention is that'ther volume of signalsreproduced byrepro'ducing de-.

vice I2 may be controlled by adjusting volume 7 control resistance 24.An adjustment of resist' ance 24 causes no substantial nonlinearitybe-xtween the intensity of input signals applied to grid I5- and theintensity of signals developed across resistance 25 over a large rangeof input "signals; The magnitudeof resistance 24 not only-determines thegain in device I!) but controlsjalso the 1 amount of space currentflowing in device -10.

Switch 45 having one of its terminals connected to the positive terminalof source 40 serves to energize and deenergize the cathodes of devicesIIl'and I4.

Switch IE-having one of its terminals connected to the positive terminalof source 23 serves to in terrupt the space current flowing in devices I0 and I4. Switches 45 and 4B-may be ganged together 7 operates as apentode and includes control electrode i 8, screen electrode 22,suppressor electrode Ifiand anode 2i). 7 1

Measurements substantiate the theory that, in r 7 efiect, there are twoamplifying stages in the V envelope of discharge ,device Ill:Withth'ed'e-= Device II], the circuit connections V The second,amplifyingstage vice adjusted for good operation, the gain realized fromcontrol electrode Hi to anode 20 was of such magnitude that, whenmultiplied b the gain realized from the grid IE to electrode 2|, anoverall gain was determined approximately corresponding to the overallamplification of the discharge device H).

The overall gain of discharge device I 0 is pref erably adjusted byadjusting the amount of regeneration in discharge device I 0. It isdesirable to make the amount of regeneration such that linear operationof the stage including device it! is assured consistent with as highgain as possible. For purposes of analysis, the two stages may beconsidered to be equivalent to two sepa rate discharge devices, a triodeand a pentode, connected in cascade, wherein the regeneration may besymbolized b a negative resistance of the dynatron type connected acrossthe anode load of the triode.

The regeneration which comes into being is believed to be due to thenegative transconductance from the second control grid I8 to the screenelectrodes 2| and 22. This negative transconductance efiect is producedin accordance with the following considerations: The total cathode spacecurrent of device I0 is substantially independent of the voltage appliedto the second control grid I8, which controls the distribution ofcurrent between electrode 2| on one side and electrode 22 and anode 20on the other side. Since the two electrodes 2| and 22 are connectedtogether, substantially equal and opposite effects are produced on theelectrodes 2| and 22 and on anode 20 by a change of the voltage on thesecond control grid It. That is, if electrode I8 is made more negative,more space current tends to flow to electrode 2| and less'to electrode22 and anode 20. trode 22, which shares its current with anode 20, isless than the increase in current to electrode 2|. Therefore, the netcurrent to electrodes 2| and 22 increases with negative potential inelec trode l8, and current to anode 20 decreases. Consequently, thetransconductance between second control grid I8 and anode 20 ispositive, and the transconductance between second control grid l8 andconnected electrodes 2| and 22 is negative. When, as in this instance,the current flowing to connected electrodes 2| and 22 produces a voltagedrop across external resistance 26 in response to variations impressedon the main control grid I5, at least a portion of. that voltage drop isfed back to the second control grid l8, through coupling capacitance 29for further controlling the electron stream in discharge device It!regeneratively by voltage on electrode I8. In Fig. 1, a negativeresistance efifect which causes regeneration for signals of audiofrequencies occurs between connected electrodes 2| and 22 and secondcontrol grid l8 considered as a But the decrease in current toelecgroup, since coup-ling condenser 29 is of low reactance for signalsof audio irequency, and the cathode of device l0.

In the particular amplifier circuit shown in the negativetransconductance between the control grid l8 and connected electrodes 2|and 22 so that the amount of regeneration in discharge device H! is alsochanged. That is, when the positive transconductance between the grid l8and anode 20 is high, the negative transconductance between control gridl8 and. connecte grids 2| and 22 is also high.

For that reason, the amount of regeneration is adjusted by adjusting theanode output resistance 25. When anode resistance 25 is decreased belowa critical resistance, the transconeductance between the control grid l8of device in and anode 20 is increased so that device I!) breaks intooscillation, due to the corresponding increase in negativetransconductance between control grid l8 and connected grids 2| and 22.The signal voltage developed across resistance 25 is, of course, equalto the signal current flowing therethrough multiplied by the resistanceof resistance 25. By making resistance 25 high the transconductance ofthe device is lowered but the voltage developed across resistance 25tends to remain constant.

It is desirable to make the resistance 25 as large as possible,consistent with high gain, not only for suppressing oscillation indevice I0 but also for decreasing the current drain from Voltage source23. Also, resistance 25 is made large so as to assure linearamplification of high in tensity signals applied between the grid l5 andcathode of device I0. Since a reduction of anode to cathode conductancetakes place when the anode potential is reduced low enough to causeoperation along the curved portion of the anode voltage-anode currentcharacteristic in some discharge devices, thisoperating condition is notdesirable for maximum gain and linearity but it may be necessary if noother means is used to suppress or control the amount of regeneration,and is desirable as means for reducing discharge current.

Another method of controlling the regeneration between the triode andpentode sections of discharge device I0 is to adjust the continuousoperating potential of connected grids 2| and 22, for example, byadjusting the resistance 26 In general, the smaller the resistance 20,the more discharge device |0 approaches a condition of selfoscillation.When resistance 26 is made large, space current in electrodes 2| and 22is reduced.

Regeneration in discharge device I0 is also affected by the amount ofelectronemission from the filament or cathode. It is not uncommon forthe regeneration in device I0 to increase with a decrease in electronemission from the cathode of discharge device Id. In other words, as theVOlt age of source 20 is decreased, for example, due to prolongedcurrent drain therefrom, the overall amplification of device It! tendsto increase and thus a compensation is provided for the loss. ofamplification resulting from the decrease in voltage of source 23 inprolonged operation of the hearing aid. Under certain conditions achange in voltage of the heating source 40 may cause a condition ofself-oscillation. Variation in the circuit behavior due to change inheating source voltage 03 is minimized greatly when resistances 25 and26 are suitably large.

A possible explanation for the increase in regeneration when filamentemission is decreased may perhaps'be that there is a reduction inemission so that all electrode potentials rise. large anode and screenelectrode resistances are used to force operation of the pentode part ofthe Sinc gain and regeneration.

when anode and screen potentials rise, the dynamic transconductance ofboth anode and screen electrode increase with a' consequent increase inThe transconductance between the electrode l 3 and anode 20 is increasedand correspondingl the negative tran'sconductance' or regeneration inthe triode stage is in creased. When resistances 25 and 25 are properlyadjusted for high gain consistent with low current consumption inaccordance with principles discussed herein, reduction of voltage ofsource 40 has appreciably no effect on operation of device Iil' over alarge range of change of voltage of source 49.

Under certain conditions of adjustment, the resistances .24 and25=mahave such relative mag nitudes that the electrons constituting the spacecharge are attracted to connected electrodes 2! and 22 and anode 20 insuch proportion that the respective positive and negativetransconductances are substantially unaltered asthe space charge isreduced when the filament emission is decreased. This has been observedwhen resistance 2515s of the, order of 700,000 ohms and resistance 26 isof the order of 80,000 ohms, device ll] being a 1R5. 7

In a-demonstration to show the maximum overall gain obtainable by usingdevice H], the plate load resistance 25 was reduced so that it wasalmost smallenough for the production of self-sustained oscillations indischarge device it. Withv l oq microvolts input; the output voltage was1.4

volts. This corresponds t an overall gain of 14,000 in one dischargedevice. Such gain is usually not conveniently usable because of thegreater diificulty of proportioning resistances 25 and 26 to avoidself-sustained oscillations as the voltage of source to drops.

8 tensityi's applied between main control grid l and the cathode ofdischarge device l0, an instantaneously decreasing currentcorrespondingly flows through resistance 25; That is, the effectivetransconductance between grid l5 and anode 20 is negative in character.This is in line with the theory that device Hlincludes two-amplifyingdevices in cascade whereinas is well known the effectivetransconductance between the grid of the tensity of signals; appliedbetween grid IE and itscathode.

When the resistance 25 is increased, the amount of regeneration indischarge device In is decreased, the amount of space current flowing toanode 2B is reduced, and consequently the overall gain is decreased.Also, when the resistance 26 is increased, the amountof space currentflowing to screens 2| and 22 is reduced, and the overall gain isdecreased. When resistance 25 or resistance 26 is made small, the spacecurrent flowing through the corresponding, resistance 2-5 or 26 isincreased, and the overall amplification increases to a point where theamplifying circuit changes abruptly into a state of self-oscillation.Just before such self-oscillation begins, amplification is great, therei is enhanced linear orirequency distortion, en-

The circuit shown in Fig. 1 has much advantage total amount approaching360 or ,a multiple thereof, including the phase shift in the amplifier.

This necessitates either carrying the phase shifting operation over twotubes, each one of which shifts the'phase 180, or using a transformerfor phase inversion. Systems incorporating such means .areiinferior instability and frequency.

range to the amplifying system as disclosedherein incorporating a singledischarge device with are sistance load, because such systems must alltransfer signalsthrough at least two filter meshes in the feedback loopto obtain the 360 phase shift through the entire feedback loop, whilethe pres-.,

ent arrangement requires but one mesh including resistances 2E and 21and condenser 29 to complete the entire feedback loop for shiftingsignals 360; or, if it be preferred, 0. That is, there is no phase shiftdesired in translation of signals through the single mesh comprisingresistances; 26 and 2'! and condenser 29, signals on grids 2!.

and ZZbeing effective to produce regeneration when impressed in phaseongrid H3; The re generative efiect is correspondingly constant over 'afrequency band limitedf only by the signal transferring ability forwhich the mesh including justed. V 1. 7 j

, When a signal of increasing instantaneous inhanced instability and theanode voltage is not 7 sufiicient to accommodate'signal voltage changes,

so that signals so greatly amplified are; distorted.

Such adjustment is undesirable. 'B making the resistance 25 verylargefor high gain and low current consumption, regeneration is reducedsufficiently that the device H! is highly linear and yet has great gainfor amplification of small signals. It is thus seen'that, in general,when the amount of space current flowing in device Ii] is also. It isunderstood, of course, that such space current flow in varying degreeisthe same as varying current drainfrom source '23.

resistances land/.27 and condenser 2% is ad- Adjustment made inincreasing the size of resistance 25 to cause more linear operation andtosuppress self-oscillation and reduce discharge current is quitedifferent from that present, in

known self-oscillation circuits having a resistance in the anodecircuit. That is, inthe amplifying oscillating circuit of a'multivibrator, having a resistance in the anode circuit,self-oscillation is suppressed when such resistance is made smaller,whereas in the arrangement shown in Fig- 1; self oscillation issuppressed by increasing resistance 25. I

With a constant output voltage across resist* linear operatingconditions. Consequently, when plate coupling resistance 25 isincreased, compensation is introduced for nonlinear conditionsprevailing when resistance 25 i small.

Since the resistances 25 and 26 influence regeneration and linearoperating conditions of device IO, and since they are connected inseparate series circuits, including the common voltage source 23, theirrelative sizes influence the operating conditions of device i0.

When resistance 25 is increased, the overall transconductance of deviceit tends to decrease; and it is then desirable to have resistance 26relatively small, consistent with linear operating conditions, so as toprovide a compensation for the loss in gain due to increase inresistance 25. That is, when the ratio of resistance 25 to resistance 26is increased, the overall gain 'of device i tends to be less afiected bya change in resistance 25 even though a greater and more linear voltageamplification is produced when resistance 25 is increased. That is, whenresistance 26 is small compared to resistance 25, greater linearity isachieved than when the resistance 25 is comparable to resistance 26.Also, when resistance 26 is small compared to resistance 25, variationsin heating voltage source 40 have little effect on the operatingconditions of discharge device H1.

The modified arrangement in Fig. 2 diifers from the arrangement shown inFig. 1 in that the space current for the anode 20 of device It] does notflow through the volume control resistance 24. In Fig. 2, the volume orgain of device In is controlled by adjusting the volume controlresistance 24 or adjusting the amount of space current flowing throughresistance 24 and to the screen grids 2| and 22.

To accomplish this type of volume control in I Fig. 2, the resistance 25has one of its terminals connected to the anode 29 of device I0 and itsother terminal connected to the positive terminal of source 23 and, asin Fig. 1, one of the terminals of volume control resistance 24 isconnected to the screen grids 2| and 22 and the other terminal ofresistance 24 is connected to the positive terminal of source 23.Otherwise, the circuit arrangements in Figs. 1 and 2 are the same.

The circuit of Fig. 1 is preferred over the circuit arrangement of Fig.2 since it is found that when in the arrangement shown in Fig. 2 theresistance 24 is increased to a relatively high magnitude, the potentialon the grids 2| and 22 decreases, the overall conductance of device I0decreases, the potential of anode 20-increases, and device l0 tends tooscillate. When, as in the preferred form of the invention in Fig. 1,space current from anode 20 and scren grids 2| and 22 flows throughvolume control resistance 24, the current flowing through anode 20 ismaintained relatively small and device I0 is less prone to oscillate.

' In Fig. 1, adjustment of gain control resistance 24 causes a directadjustment in the continuous potential of anode 20 and screen electrodes2| and 22 and causes a change in overall gain of device In In Fig. 2,adjustment of gain control resistance 24 causes an adjustment in thecontinuous potential of screen electrodes 2| and 22 and causes a changein overall gain of device I 0, and, of course, the anode potential ischanged in the opposite sense in accordance with the aboveconsiderations.

It has been found that with the volume control arrangement shown in Fig.1, a more suitable 10 range of volume control may be produced with agiven size volume control and, more important, the minimum gain ofdevice I!) may be made small.

A particular feature of the present invention resides in the arrangementof volume or gain control resistance 24 in relation to the other circuitelements shown in Figs. 1 and 2. Resistance 24 serves not only tocontrol the gain of device I0 without causing self-sustainedoscillations in device IE), but also serves to limit the amount of spacecurrent flowing through device In. This feature is of particularimportance in battery operated hearing aid circuits wherein the cost ofreplenishing batteries is of importance. That is, resistance 24 is acombination gain control and current limiting or battery saving device,In general, the smaller the gain of the amplifying stage It, the smalleris the amount of space current flowing in device l0 so that the user ofthe hearing aid circuit shown herein controls to a certain extent theamount of current from battery 23.

While the two preferred methods for controlling the gain of device |0are shown in Figs. 1 and 2, it is understood that other means may beemployed for controlling the gain of device I0. For example, the gain ofdevice Ill may be controlled by varying the magnitude of resistance 21as shown in Fig. 3, or by varying the magnitude of resistance 25 asshown in Fig. 4, or by varying the magnitude of resistance 26 as shownin Fig. 5,

or by applying a fractional part of the voltage appearing acrossresistance l6 between grid I5 and cathode of device ID as shown in Fig.6, or by applying a fractional part of the voltage appear-- ing acrossoutput resistance 32 between the main control grid and cathode of deviceM as shown in Fig. '7.

Although the modifications in Figs. 3 to 7, inclusive, show other meansfor controlling the gain of device IE, it is understood that thearrangements shown in Figs. 1 and 2 are preferred in that order, because(1) a greater control is available for controlling the amount ofregeneration in device l0, especially when the magnitude of source 40becomes relatively small, and (2) the user may exert some control overthe amount of space current flowing through device Hi.

In a practical embodiment of the present invention, the various circuitelements described herein had the following properties: discharge deviceIll-1R5 R, C. A. type, resistance |G--5 megohms, resistance 24-400,000ohms, resistance 25-680,000 ohms, resistance 26-68,000 to 82,000 ohms,resistance 2'|10 megohms, resistance 32- 4.7 megohms, condenser 28--.lmicrofarad, condenser 29-100 micromicrofarads, condenser 3|- .001microfarad.

While the particular embodiments of the present invention have beenshown and described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects, and therefore the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of this invention.

I claim:

1. A substantially linear high gain amplifier circuit including anelectron discharge device having a cathode, a main control grid, asecond control grid, an electrode and an anode, means for supplyingspace current between the anode and cathode of said discharge device,means including the electrode and second control grid. for prol g ne tres stance gect s id s cond 6. mm rid. be n a ran ed to. ha .mu ancrespect to said electrode whereby the negative transconductance of saidelectrode causes regenoration, and a variable combination space currentlimiting and gain control resistance connected in se ries bircuit withsaid electrode and with said anode to control smiultaneously the flow ofcontinuo-us space current to said electrode and anode.

,2. A substantially linear high gain amplifier circuit includingelectron discharge device having a cathode, a main control grid, asecond control grid, an electrode and an anode, means for supplyingspace current between the anode and cathode, of said discharge device,means for supplying space current between the electrode and cathode "ofsaid device, means, for impressing avoltage from said electrode on saidsecond control grid, said second control grid being rranged to havesimultaneously a positive transconduct ancewith respect to the anode anda negative transconductance with respect to the electrode, whereby thenegative transconductance of said ec r d s su h as o ause re eneration.in sl phase as to cause self-sustained oscillations, means for.impressing signal voltages between said main control grid and cathode,means. coupled to said anode for developing output signal voltages meansfor reducin said regeneration whereby the intensity of saidjoutputsignals varies substantially linear with the intensity of the inputsignals over the range of, input signals, and variable resistance meansconnectedseriallywith aiflail deand said e ectrode to adjust s multaously the flow of continuous space current to said electrode and anodeto control the gain oi"v said amplifier circuit.

3. A substantially linear high gain amplifier circuit including anelectron discharge device having; a cathode, a main control. grid, a.second control grid, an electrodeand ananode, a Voltage sourceconnectedbetween the;cathode and anode fordelivering space current tothe dischargerdevice, means arranged tosupply space'current to saidelectrode means for applying, input. signal voltages between the maincontrol grid and cathode, coupling means. between said electrode andsecond control grid, said secondlcontrol grid being arranged to havesimultaneously. a positive transconductance with respect, to the anodeand a negative transconductance with respect. to:said electrode wherebythe negative transconductance of said electrode causes regeneration, ahigh resistancecoupled to the anode. forhigh gain and for limiting thecurrent flow in the discharge device, said resistance aiiecting saidpositiveand negative transconductance, and a variable combinationspacecurrent limiting andgain control resistance connected in series circuitwith said electrode and saidanode to adjust. simultaneously the flowof,continuous space current to said electrcdeandanode to controlthe gain ofsaid amplifier circuit.

4. An amplifier circuit including an electron '12 hac auce lement.connected etween aid' two spaced elcctrodesiand the second controlgrid'a re stan e clc nt connected between the second control gridcathode, a combination coup and voltagedropping resistance havingonezof: its terminals connected to. said'two. spaced electrodes, acapacitance element vccnnected between the t o e and oth r terminal. ofthe-lastnientioned resistance, a combination coupling and voltagedropping resistance having one of its terminals connected to the anode,a, third voltage dropping resistance, a voltage source'for supplyingspace current to said discharge device, said voltage source beingconnected between'the' cathode and anode-through a series circuitincluding the second and third mentioned voltage dropping resistances,said voltagev sourcelbeing connected: be.- tween the, cathode, and saidtwo. spaced electrodes through a series circuit including theffirst andthird mentioned voltage droppingj resistances, and means for utilizingthe voltagedrop across said resistance connected tothe anode, said thirdVoltage dropping resistance beingvariable for'ad's justing the gain inthe amplifying circuit.

5. A substantially linear high. gain amplifier circuit including anelectron discharge device having a cathode, a main control grid, asecond control grid, an electrode andan anode, means for supplying spacecurrent between the anode and the cathode of said discharge device,means including the electrode and second control grid for producing anegative resistance efiect, said second control gridbeing arranged-tohave simultaneously a positive transconductance with respect to theanodeand a negative transconductance with. aid electrode whereby the negativetransconductance of said electrode causes regeneration, and acombination space current limiting and gain control resistance connectedin series circuit with said electrode and with said anode to control theamount of continuous space current flowing thereto. H

6. A substantially linear high gain amplifier circuit including anelectron discharge device having. a cathode, a'main control grid, asecond control grid, an electrode, and-an anode, a voltage sourceconnected between the cathode and anode for delivering space current tothe discharge device, means for applying input signal voltages betweenthe main controlgrid and oathode, coupling means between said electrodeand second control grid, said second control lid being arranged to havesimultaneously a positive transconductance with respect to theanode anda. negative transconductance with respect to said,

electrode whereby the negativetranscqnductance of said electrode causesregeneration, a high reisistance couplcd-tothe anode for-high gainaudfor. limiting the current fiow in the. dischargede vice, said resistanceaffecting said positive and negative transconductance, and a,combination discharge device, said electron discharge device,

having a cathode, a main control grid, 2. suppressor grid and an anode,said suppressor grid-being connected to the cathode, two spacedelectrodes connected togetherand disposed between the suppressor-gridand-main control grid,.atsecond. control, grid disposed between, the twospaced electrodes, means for applying a. signal voltage. bee

tween themain control gridand, cathode, a ca-.

space current limiting and gain control resistance connected in seriescircuitwith said electrodeand,

said anodeto control the'a mount otcontinuous space current flowingthereto. 4

7. An electron discharge device. including. 'a source ofz-electronsand afirst anode, a central electrode and a seconcl'anode mounted;inthatvorder. at. increasing distances, respectively, from said source,saidifirst anode beingcoupled ex,- ternally to said control electrode,whereby current changes in-said first'anode are reenforcedby action ofsaid control electrode, a source of operating potential forsaid;firstand secondanodes, said last mentionedsource having a nega- 13i4 tive terminal connected With-said electron source REFERENEES CITEDand a positive terminal first and Second limped The following referencesare of record in the ances connected between said positive terminal fileof this patent:

and said first and second anodes, respectively, and

means for simultaneously varying the impedance 5 UNITED $TATES PATENTSbetween said terminal and said. first anode and Number Name Date theimpedance between said terminal and said 2,22 030 Herold Jam 7 1941second anode in the same sense and at substan- 2,342,492 Rankin at Feb,22 1944 tially the same rate, whereby the ratio of said 2,226,561 HeroldDec. 31, 1940 impedances is maintained within a predetermined 102,287,280 Terman June 23, 1942 range of funpedances, 2,235,817 FreemanMai. 25, 1941 2,262,916 Boucke Nov, 18, 1941 GILBERT E. GUSTAF'SON.2,214,614 Hunt Sept. 10, 1940

